Wi-Fi, also referred to as Wireless Local Area Network (WLAN), uses IEEE 802.11 standards as an air interface (including physical and Media Access Control (MAC) layers). In IEEE 802.11, the communication channel (also commonly referred to as communications medium) is shared by stations under distributed channel access (DCA) using a function called distributed coordination function (DCF), which is based on a carrier sense multiple access with collision avoidance mechanism (CSMA/CA).
The DCF uses both physical and virtual carrier sense functions to determine the state of the communications medium. The physical carrier sense resides in the physical layer (PHY) and uses the energy detection and preamble detection to determine whether the communications medium is busy. The virtual carrier sense resides in the MAC layer and uses reservation information, e.g., a network allocation vector (NAV), in a duration field of MAC headers announcing impeding use of the communications medium. The communications medium is determined to be idle only when both the physical and virtual carrier sense mechanisms indicate it to be so.